1. Technical Field of the Invention
The present invention relates in general to clock synchronization, and in particular, to clock synchronization within mobile backhaul networks.
2. Description of Related Art
The wireless infrastructure market is migrating towards 3G, replacing traditional Base Transceiver Station (BTS) and Base Station Controller (BSC) elements with UMTS Node B (base station) and RNC network elements. With the migration towards 3G underway, the T1/E1 links traditionally connecting the BTS to the BSC are also being replaced with packet switched mobile backhaul networks that provide connectivity between the base station and the RNC. To deliver traditional T1/E1 voice and data service across the new IP-based mobile backhaul networks, pseudowires are often used. A pseudowire is an emulation of a native service, such as T1/E1, over a packet switched network (PSN), such as an IP-based Multi Protocol Label Switching (MPLS) network. Pseudowires emulate the operation of carrying the native service by segmenting, adapting and encapsulating the T1/E1 traffic into packets of the format required by the PSN.
The term “pseudowire” (PW) typically refers to a PSN tunnel that both originates and terminates on the same PSN. Thus, a PW passes through a maximum of one PSN tunnel between the originating and terminating Provider Edge (PE) routers. To extend the pseudowire service through multiple PSN tunnels (or multiple network segments), multi-segment pseudowires (MSPW) are used. A MSPW is a static or dynamically configured set of two or more contiguous PW segments that behave and function as a single point-to-point PW. Thus, a MSPW can be considered a single PW that is segmented into a number of concatenated hops.
Protection for the network connection between two PE routers (e.g., the RNC and the base station) within the IP-based mobile backhaul network is typically achieved by using a primary single PW or MSPW and one or more secondary PW or MSPWs on standby in order to provide redundancy. In addition, protection for the clock distribution network between the RNC and base station within the IP-based mobile backhaul network is typically achieved by providing both a primary master clock and a secondary master clock at the RNC, each of which is able to communicate with a slave clock on the base station.
However, there is currently no redundancy for the slave clocks. Therefore, upon a failure of the primary master clock on the RNC, the slave clock on the base station must resynchronize with the secondary master clock on the RNC. Likewise, upon a failure of the primary MSPW between the RNC and the base station, the slave clock must switch-over to the secondary MSPW. In both cases, the slave clock may drift from the system clock, potentially resulting in dropped calls in the mobile backhaul network.
In addition, there is a lack of delay and/or packet loss awareness for protection switching in redundant PW's that deliver clock synchronization. Degradation in performance of the primary PW can negatively affect not only the distribution of the clock, but also the synchronization of the entire clock system.